This invention relates generally to clothes washing machines and more particularly to a washing machine having a suspension system capable of moving relative to the cabinet.
As is known in the art, washing machines may vibrate under certain operating conditions, and, in aggravated cases may even move (or "walk"). The noise level of the washer operation often increases significantly when such vibration occurs. This undesirable vibration occurs generally when the forces exerted on the washer's supporting feet exceed the resistive frictional forces between the supporting feet and the floor. Such a condition may be referred to generally as causing "frictional" mode vibration. One specific operating condition under which frictional mode vibration occurs is when the rate at which the washer's tub assembly is rotated, during a spin drying cycle for example, is the same as the natural or resonant frequency of the washer. This type of vibration may thus be referred to as "resonant" mode vibration. Note that while washers have various associated natural or resonant frequencies, such as that corresponding to the spring constant of the suspension springs and that associated with the mechanical system comprising the washer and floor, it is the latter natural frequency that often corresponds to the spin rate, thereby causing resonant mode vibration.
As is also known in the art, the natural frequency associated with a washing machine/floor system is a function of, inter alia, the moment of inertia of the machine, the spring constant associated with the floor (i.e. a function of the floor's stiffness), and the spring constant associated with the washer (i.e. a function of the stiffness of the particular washer's structural components).
One way known in the art to reduce the tendency of the machine toward resonant mode vibration is to design the machine so that the natural frequency associated with the washer/floor system does not correspond to the spin speed. For example, this natural frequency can be increased by decreasing the moment of inertia of the cabinet and base, such as by using plastic rather than metal tubs. While this technique may increase the washer/floor natural frequency, in some cases above the spin speed, it does not eliminate the resonant vibration problem for all expected home floors given the variation in the spring constants of such floors.
Other techniques for reducing such vibration were suggested in Consumer Reports Magazine, February 1991, page 116, including the use of a thick plywood panel under the washer or stiffening the floor joists. In this way, the spring constant of the floor (and the washer/floor natural frequency proportional thereto) is increased. While this technique may assist in reducing a machine's tendency toward resonant vibration, it may be costly and inconvenient to practice.